Osmotic devices for delivering a beneficial agent to an environment of use are known to the prior art in U.S. Pat. No. 3,845,770 issued to Theeuwes and Higuchi, and in U.S. Pat. No. 3,916,899, issued to the same patentees. The osmotic devices disclosed in those patents comprise a semipermeable wall surrounding a compartment containing an agent. The wall is permeable to the passage of an external fluid, and it is substantially impermeable to the passage of agent. The devices have a passageway through the wall that connects the compartment with the exterior of the device for delivering the agent from the device. These devices deliver an agent by imbibing fluid through the wall into the compartment, at a rate determined by the permeability of the wall and the osmotic pressure gradient across the wall, to produce an aqueous solution containing agent that is delivered through the passageway from the device. The devices are effective for delivering an agent that is soluble in fluid imbibed into the compartment, thereby forming a solution of the agent that is delivered from the device, and also for delivering an agent that is poorly soluble in the fluid and is mixed with an osmotically effective solute that is soluble in fluid imbibed into the device, thereby forming a solution of the solute containing agent in suspension that is delivered from the device.
The prior art devices described above represent an outstanding and a pioneering advancement in the delivery art, and they are useful for delivering innumerable agents to many environments of use. It will be appreciated by those versed in the art, that the usefulness of the devices can be increased, and their application broadened, if a device and method are provided for improving the delivery characteristics of certain agents that are difficult to deliver from osmotic devices. For example, both the use and the value of a device would be unexpectedly increased, if (1) a device and a method are provided that during the operation of the device, the solubility of an agent that is poorly soluble in the fluid is enhanced, such that it no longer requires an added osmotically effective solute for its delivery as the agent now operates as its own osmotically effective solute for its delivery from the device, and (2) if the solubility of an agent that is too high in the fluid and delivered in excessive amounts in a short time is decreased in the fluid, such that the agent can now be delivered at a meaningful rate and over a prolonged period of time.